1. Field of the Invention
The present invention relates to a method of processing (e.g., rinsing) a substrate with pure water or ultrapure water, and especially relates to a substrate processing method of processing a substrate while suppressing electrostatic charge of a structure (e.g., a dielectric film, a metallic film, or a device including a dielectric film and a metallic film) formed on the substrate.
2. Description of the Related Art
In a manufacturing process of a semiconductor device, various films having different physical properties are formed on a silicon substrate and these films are subjected to various processes, thus forming fine metal interconnects. For example, in a damascene interconnect forming process, interconnect trenches are formed in a film, and the interconnect trenches are then filled with metal. Thereafter, an unnecessary metal is removed by chemical mechanical polishing (CMP), so that metal interconnects are formed. A variety of films including a metal film, a barrier film, and a dielectric film exist on a surface of the substrate that has been manufactured through such a damascene interconnect forming process.
A CMP apparatus (polishing apparatus) for polishing a substrate typically includes a substrate cleaning apparatus for cleaning and drying a polished substrate. Cleaning of the substrate is performed by bringing a cleaning tool, such as a roll sponge, into sliding contact with the substrate while rotating the substrate. After cleaning of the substrate, ultrapure water (DIW) is supplied onto the rotating substrate, thereby rinsing the substrate. Before the substrate is dried, the ultrapure water is further supplied onto the rotating substrate to rinse the substrate.
It is commonly known that the ultrapure water, to be supplied onto the rotating substrate, has a high specific resistance value (≧15M Ω·cm) and that the surface of the substrate is electrostatically charged by the contact with the ultrapure water. Practically, experiments have confirmed that the surface of the substrate, on which metal interconnects and dielectric films are formed, is electrostatically charged as a result of the contact with the ultrapure water. Possible causes of such a phenomenon of the electrostatic charge may include the fact that the ultrapure water has a high specific resistance value and that the ultrapure water forms a flow on the rotating substrate, although the causes are uncertain. The electrostatic charge of the substrate surface may cause reattachment of particles that have been once removed by the cleaning process of the substrate surface, and may cause destruction of devices due to electrostatic discharge. Further, in devices having copper interconnects, copper (Cu) itself is liable to migrate under the influence of the surface charge, and may be attached to a dielectric film. Consequently, shortcut between the interconnects or leakage of current may occur, and/or poor adhesion between the copper interconnects and the dielectric film may occur.
Since the electrostatic charge of the substrate surface can lower a reliability of the devices, it is necessary to eliminate static electricity from the substrate. However, once a dielectric film, such as a TEOS film, is electrostatically charged, it is extremely difficult to remove the static electricity from the dielectric film. FIG. 1 is a graph showing results of an experiment for removing the static electricity from a TEOS film and PVC (polyvinyl chloride). In this experiment, ultrapure water was supplied onto a substrate having a TEOS Elm formed on a surface thereof, and onto a substrate having PVC formed on a surface thereof. The substrates were then irradiated with soft X-rays. A surface potential [V] of each substrate was measured before and after the soft X-ray irradiation. As can be seen from FIG. 1, the static electricity was removed from the PVC by the soft X-ray irradiation, while the static electricity was not removed from the TEOS film by the soft X-ray irradiation.
FIG. 2 is a graph showing results of an experiment for studying a change in a surface potential of a substrate with soft X-ray irradiation time. In this experiment, the ultrapure water was supplied onto a substrate having a TEOS film formed on a surface thereof, and the substrate was then irradiated with soft X-rays. A surface potential [V] of the TEOS film was measured after the substrate was irradiated with the soft X-rays for 30 seconds, 60 seconds, and 90 seconds. FIG. 2 also shows results of an experiment as a comparative example. In this comparative example, the ultrapure water was supplied onto the substrate, and then the surface potential [V] of the TEOS film of the substrate was measured without irradiating the substrate with the soft X-rays. As can be seen from FIG. 2, the surface potential of the TEOS film does not change regardless of the soft X-ray irradiation time. Moreover, the surface potential hardly differs between the case where the substrate was irradiated with the soft X-rays and the case where the substrate was not was irradiated with the soft X-rays. This means that the static electricity cannot be removed from the TEOS film by the soft X-ray irradiation.